Many efforts have been put forward to enhance the thermoelectric properties of AgPbSbTe (LAST), which is one of advanced thermoelectric materials with quaternary elements. In this paper, Te and Sb were completely substituted by Se and Bi respectively and the samples of AgmPb100BimSe100+2m system including different proportion of ingredients were prepared through melting and spark plasma sintering. We found that the total thermal conductivity can be largely reduced from 4.7 to 1.1 W m−1 K−1 at room temperature with increasing m values in AgmPb100BimSe100+2m. As a result, a ZT value of ~0.86 at 923 K was achieved when m = 10. These results indicate that AgmPb100BimSe100+2m system is very promising for thermoelectric (TE) energy conversion application.